1. Field of the Invention
The invention relates to a lens module, more particularly to a lens module with a fixed focal distance.
2. Description of the Related Art
As shown in FIG. 1, a conventional lens module 1 comprises a circuit board 11, a hollow lens seat 12 disposed on the circuit board 11, a lens unit 13 disposed on the lens seat 12, and an image sensor unit 14 disposed in the lens seat 12. The image sensor unit 14 is disposed on the circuit board 11 and is electrically connected to the circuit board 11 through a plurality of conducting wires 141. The lens unit 13 is disposed above the image sensor unit 14 and includes a lens barrel 131, a lens set 132, and an infrared ray filter 133. The lens set 132 gathers incoming light such that the image sensor unit 14 is able to capture an image. The infrared ray filter 133 is disposed between the lens set 132 and the image sensor unit 14, and filters out infrared rays in the incoming light that is reflected by the object to be photographed, thereby improving the image quality.
The construction of the conventional lens module 1 is based on a fixed focal distance, i.e., the distance between the lens set 132 and the image sensor unit 14 is fixed. Moreover, the lens unit 13 is secured to the lens seat 12. The aforementioned design of the conventional lens module 1 results in a relatively simple structure and a relatively small size. The conventional lens module 1 is thus currently adopted by most commercially available camera phones.
In the conventional lens module 1, the image sensor unit 14 is fixed on the circuit board 11 through a solder. The uneven spread or the thermal expansion and contraction of the solder can cause the image sensor unit 14 to deviate from a flat state relative to the circuit board 11, and can result in tilting of the image sensor unit 14 relative to the lens unit 13. Therefore, the object to be photographed can not be imaged clearly on the image sensor unit 14 without distortion, and the image quality is adversely affected. In addition, the lens seat 12 supports the lens unit 13 on the circuit board 11, and keeps the distance between the lens unit 13 and the image sensor unit 14 fixed. However, since the height of the lens seat 12 may not be precisely controlled, the position of the lens unit 13 on the lens seat 12 has to be adjusted during production, thereby resulting in a relatively high cost of manufacturing and in a relatively long production cycle.